Gasdruckschwingungsverteilung im Arbeitskanal von Seitenkanalverdichtern

The magnitude of energy transfer in side channel compressors depends on intenseness of gas pressure oscillation and transport of specific momentum in the side channel. For analysis of energy transfer from impeller to gas, the static pressure distribution and the intenseness of gas pressure oscillation in meridian profile of the side channel subject to radius and also to axial distance to impellers grid was measured with a high tightness of reading points. In order to plot the intenseness of gas pressure oscillation in meridian profile of the side channel, gas pressure oscillation in side channel has been characterized by RMS, peak value and amplitude value of gas pressure oscillation at blade rotation frequency. The results of gas pressure oscillation and tangential velocity progression in side channel from laser measurement show that the strongest gas pressure oscillations and highest velocities appear in outer region of the impeller and side channel, which refer to intense energy transfer in this region.     

Grenzbereiche von Seitenkanalverdichtern im Vakuumbetrieb

The kinematic viscosity of the gas rapidely rises with decreasing suction pressure in the vacuum region, which leads to a decrease of the reynolds number of the flow in the side channel and to a laminar flow structure which may cause a modification of the side-channel-compressor behavior during the energy transfer. By the reduced density of the gas in the vacuum region of the side channel compressor the mass flow and the transfered specific enthalpy are decreased with constant volume flow. Through that, the specific growth of enthalpy during the compression and during the expansion of the mass flow in the breaker decreases. This leads to a decrease in the growth of the temperature during the compression at the same pressure ratio and the thermal load of the compressor is reduced. The polytropic change of state of the gas during the compression approaches an adiabatic change of state for decreasing suction pressure in the vacuum region. The polytropic change of state of the expansion flow in the breaker approaches the theoretical expected isothermal change of state for decreasing suction pressure, whereby side channel compressors are relieved of thermal load and higher pressure ratios are within reach. So the breaker of the side channel compressor, which causes in pressure operation mode high specific dissipation losses and leads to high polytropic exponents effects in the higher vacuum region thermodynamic advantages of the pressure region.     

Thermodynamische Belastung von Seitenkanalverdichtern im Vakuumbetrieb

Like all turbo machines and rotating displacement machines side channel compressors are able to work in the pressure region and in the vacuum region. At present side channel compressors are used in vacuum operation only for the low vakuum region with an absolute suction pressure down to p_s = 10 kPa. The benefits of side channel compressors with the expansion flow in the breaker clearly grow contrasting the pressure operation mode and contrasting other compressor constructions with decreasing suction pressure. Therefore it is appropriate to make the working range of side channel compressors accessible also for the operation in the higher vacuum region down to the fine vacuum region because in this way side channel pumps open the possibility to cover the whole vacuum region from fine vacuum up to atmospheric pressure. This offers the advantage of using only high-speed turbo compressors in the vacuum region which have small construction dimensions, are simple designed and work lubrication free. These advantages also meet the desire of the vacuum technology for oil free delivery of gases and drawing off fumes.     

Spezifische Energieverteilung im Kanal von Seitenkanalverdichtern

Distribution of energy in the channel of side channel compressors With dynamic pressure sensors, the total pressure and dynamic pressure share can be measured in any density of the side channel profile. The dynamic progression of gas pressure, which appears as gas pressure oscillation, can be characterized by peak value of gas pressure oscillation, RMS and amplitude value p_A of gas pressure oscillation at blade rotary frequency. Out of it, the regions of intense transport of specific momentum and intense energy transfer in side channel can be ascertained. Out of the distribution of velocity in side channel profil in association with the distribution of pressure, the distribution of specific energy in side channel can be ascertained as well.     

Druckverlauf und Gasdruckschwingung im Schaufelkanal von Seitenkanalverdichtern

The pressure in the impeller, in the side channel and in the breaker of a side channel compressor with the polytropic compression and with the polytropic expansion of the breaker mass flow was investigated experimentally, and the occurring shock waves were detected during the expansion of the gas in the breaker. Thereby different pressure flows occur at the four measuring points in blade channel on the blade pressure and suction side of the related radius from r _i /r ₂=0.80 and r _i /r ₂=0.95, which give an indication of the blade channel flow. In addition to the periodic increase in pressure and the gas expansion in the breaker, the superimposed pressure oscillation in the side channel is caused by the blade rotation frequency. This superimposed pressure oscillation can be decomposed by Fourier transformation in the two pressure oscillation components. These phenomena are the reason for the more accurate investigation of the pressure flow in the blade channel during the polytropic compression and expansion of the breaker mass flow. The gradient of the effective values of the gas pressure oscillation in the blade channel leads not only to the operating characteristics of the side channel compressor ??p=f(?,n), but also to the breaker curve characteristic ??p _U =f(?,n).     

Strömungstechnisches und thermodynamisches Verhalten von Seitenkanalverdichtern im Vakuumbereich

Because of the lower gas density side channel compressors perform in vacuum operation better fluidic performace than in pressure operation for generating overpressure. The thermal load of the compressors is reduced by the lower final compression temperature. The polytropic expansion of the lower mass flow in the breaker, which removes thermal energy both from the expanding gas and from the housing and therefore causing a cooling of the compressor, contributes especially to the varied thermodynamic performance in vacuum operation. This inner thermodynamic performance of the compressor in the breaker area and the suction area provides together with the lower power absorption an advantageous performance of side channel compressors in vacuum operation at absolute pressures p _S=10 to 40 kPa. These advantages in operation and thermodynamic advantages are as bigger as higher the vacuum and as lower the gas density get. From this a promising development of side channel compressors as vacuum pumps also in a higher vacuum region can be deduced.     

Entwicklungstendenzen von Seitenkanalverdichtern

In the field of the low vacuum engineering with pressures down to p_s = 10 kPa regenerative blowers are increasingly used due to their delivery of a steady pulsation-free gas volume flow, their simply design and their small dimensions because of high pressure coefficients compared with other generators of vacuum. At present they reach absolute suction pressures of p_s = 40 kPa (400 mbar) with the single-stage type and p_s = 10 kPa with the multi-stage type with the limiting pressures still not reached. The pressure ratio of single-stage compressors and especially that of multistage compressors can be considerable raised by increasing of now archieved peripheral speed so that in the vacuum field pressure ratios up to π = 50 with absolute suction pressures of p_s = 2 kPa are within reach. These trends in design are shown and justified.     

Über die Strömung durch Turbomaschinen mit Potential im Meridianschnitt

Zusammenfassung Zum Berechnen der Str?mung durch die Schaufeln einer Turbomaschine wird ein neues Verfahren vorgeschlagen, bei dem man zun?chst die radiale und die axiale Geschwindigkeitskomponente aus der Potentialstr?mung ermittelt, dann die hierzu passende Schaufelform berechnet und schlie?lich hiermit die tangentiale Geschwindigkeitskomponente der wirbelbehafteten Str?mng erh?lt. Der Verfasser war Stipendiat der Alexander-von-Humboldt-Stiftung am Pfleiderer-Institut für Str?mungsmaschineu der Technischen Hochschule Braunschweig.     

Schalldruckverteilung in Seitenkanalverdichtern

ZusammenfassungIn Seitenkanalverdichtern arbeitet das Laufrad mit hoher Schaufelzahl am Rand des torusförmig am Umfang angeordneten Seitenkanals mit instationärer Strömung. Dabei durchläuft das Schaufelgitter das gesamte instationäre Druckfeld von p _S bis p _D sowie den Unterbrecher mit der Gasexpansion, der den Saugstutzen vom Druckstutzen trennt. Dadurch entstehen im Seitenkanal und besonders an den Unterbrecherein– und Austrittskanten Gasdruckschwingungen, die das Verdichtergehäuse zu mechanischen Schwingungen anregen und die auch als Schalldruck an die Umgebung abgestrahlt werden. Durch die große Schaufelzahl von z=36 bis 80 treten bei Antriebsfrequenzen von f=50 Hz und 60 Hz hochfrequente störende Geräusche von f _S=z f=1,8 bis 4,80 kHz auf, die als tonale Komponenten im Frequenzspektrum des Schalldruckpegels auftreten. Die störenden Geräusche, insbesondere die tonalen Anteile bei den erregenden Drehfrequenzen von f=50 Hz und 60 Hz können durch strömungstechnische und konstruktive Maßnahmen gemindert werden.In side channel compressors the impeller with high blade number works marginal of the circular at the perimeter disposed side channel with unsteady flow. Thereby the impellers grid with high blade number passes through the entire unsteady pressure field from p _S to p _D and the breaker with gas expansion, which separates inlet from outlet. Thus gas pressure oscillations accrue in side channel and especially at the breakers edges of entry and exit, which cause vibrations of the compressors casing and also are beamed as acoustic pressure to the environment. Because of the high blade number from z=36 to 80 at propulsion frequencies of f=50 Hz and 60 Hz high frequency disturbing noises of f _S=z f=1,8 to 4,80 kHz occur, which manifest as tonal components at these frequencies in frequency spectrum of acoustic pressure level. The disturbing noises, especially tonal components at rotary frequencies of f=50 Hz and 60 Hz, can be diminished by fluid mechanical and design features.     

Einfluß der Unterbrechergeometrie auf die Arbeitsübertragung und den Wirkungsgrad von Seitenkanalverdichtern

Zusammenfassung Zur Trennung von Druck- und Saugseite des Seitenkanals ist ein Unterbrecher erforderlich, der das direkte überstr?men des verdichteten Gases verhindert. Der Unterbrecher bewirkt aber nicht nur die Abdichtung, sondern er beeinflu?t auch wesentlich den Expansionsvorgang des überstr?menden Unterbrechermassestromes und damit wiederum den Verdichtungsvorgang im Seitenkanal. Um den Einflu? der Unterbrechergeometrie auf diese Vorg?nge zu ermitteln, wurden unterschiedliche Unterbrechermodule in einem Seitenkanalverdichter bei Druck- und Vakuumbetrieb untersucht. Der Umfangswinkel des Unterbrechers und die Oberfl?chengeometrie beeinflussen den Expansionsvorgang und den polytropen Kupplungswirkungsgrad unterschiedlich im Bereich von η=0,41 bis 0,49. Damit ist aufgezeigt, da? eine Optimierung des Unterbrechers notwendig ist, um m?glichst adiabate Zustands?nderungen im Seitenkanalverdichter zu erreichen. Der relative Unterbrecherwinkel soll für Schaufelzahlen von 40 bis 60 α_U/2π=0,115 bis 0,135 betragen.     

Anteil des Schalldruckes an den Gasdruckschwingungen in Seitenkanalverdichtern

Machines and plants operating within the vicinity of people need to be subjected to noise investigation and reduction. This includes the fans, pumps and the compressors. It is known that only a small part of the pneumatic oscillations, which result from turbulence, current exchange or by strong expansion currents are emitted as effective sound pressure and released into the environment. Although there are several mathematical models on the origin and propagation of sound, the audible amount of turbulence and/or pressure oscillation has not been known until now. These ratio values can be determined by parallel measurements of the pneumatic oscillation in a machine and of the effective sound pressure on the acoustic sources in relation to the distance to the acoustic source and the operating parameters of the compressor. The following contribution determines these values for a side‐channel compressor.     

Druckschwingungsverteilung im Seitenkanal von Verdichtern

Distribution of the pressure oszillations in the side channel of compressors The investigation of the unsteady pressure field in side channel machines with high pressure coefficients of ψ_n = 3,5 to 34 gives a better understanding of the unsteady turbulent vorticity flow in the impeller and the side channel and also of the energy transfer. The impeller with high number of blades generates a turbulent vorticity flow, which exists over the entire side channel. The specific momentum causes pressure oscillations of p(t) = 250 Pa to 9,0 kPa also in the entire side channel which lead to an increase of the static pressure in the circumference of the side channel. The oscillation of the pressure is exited by the blade passage frequency and the frequency of the turbulent vorticity flow, with the lower frequencies having priority to the energy transfer. It also leads to dissipation losses limiting the efficiency and causing a heat up of the gas.     

Versagen von Keramik im Hochtemperaturbereich

Failure of ceramics at high temperatures Failure of ceramic materials at high temperatures is very complicated. At low temperatures the failure of ceramics is governed by subcritical crack growth under quasistatic and cyclic loads. In the high temperature region the effects of creep crack growth and creep fracture have to be considered, too. The main part of the paper is addressed to the effects of subcritical crack growth and creep crack growth. The application of the fracture mechanical C*-concept is discussed in detail.     

Zur Kennlinienstabilität von Seitenkanalverdichtern About the stability of the characteristic curves of side channel compressors

In contrast to radial and axial turbocompressors side channel compressors have stable operation characteristics in the entire operation range. Up to now this attribute, which is advantageous for the operation of side channel compressors was just taken without questioning the reasons. For stable operation characteristics of turbomachiery in the widening of the characteristic field in the part-load region are aspired and demanded by many fields of application, in this document the reasons for this phenomenon in side channel compressors shall be investigated with the aim of using the responsible flow structures in other types of compressores too and of extending the safe operation range. The question has to be answered whether stage of side channel compressors are able to enforce a stable characteristic curve in a combined compressor unit when coupling with stages of other types of compressors. If side channel compressors are able to, extending the operation ranges of turbocompressors by side channelexhaust stages without surge are within reach.     

Zustandsänderung und Aufheizung des Gases in Seitenkanalverdichtern

Zusammenfassung Seitenkanalverdichter unterliegen trotz ihrer geringen Druckverh?ltnisse im Teillastbereich erheblichen thermischen Belastungen. Dadurch steigt nicht nur die Verdichtungsendtemperatur und die Maschinenbelastung, sondern mit steigender Maschinentemperatur erfolgt auch eine erhebliche Aufheizung des Gases bereits im Eintrittsbereich, wodurch die Arbeitsübertragung beeinflu?t wird. Die Resultate experimenteller Untersuchungen zeigen, da? die Aufheizung des Gases besonders im Eintrittsbereich des Seitenkanals erfolgt und dadurch die Arbeitsübertragung im vorderen Bereich stark verlustbehaftet erfolgt. Die Folge davon sind sehr hohe Polytropenexponenten bei gro?en Druckverh?ltnissen im Teillastbereich, die zu einer gro?en W?rmezufuhr an das Gas führen und den Wirkungsgrad der Maschinen mindern.     

Betriebsfeste Bemessung von Stahlkonstruktionen im Anlagenbau

Design against Operational Strength of Steel Constructions for Plants The knowledge of operational loading, shape, material and manufacturing of components for plants is necessary for their design. While loads and geometry determine the overall and local stresses, the stressability is given by the material selection and manufacture. Herefore, different design concepts and evaluation criteria are used. The numerical strength proof-out is supported by particular quality requirements in the material provision, design, manufacture and control, and if possible by load and strain measurements during service. Especially, for safety components the predicted fatigue life must be assured by inspections during their maintenance.